Metal ceramic product



METAL CERAMIC PRODUCT Louis A. Conant, Indianapolis, Ind., assignor to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Application May 19, 1954, Serial No. 430,987

20 Claims. (Cl. 29-1825) This invention relates to metal ceramics and refers more particularly to novel metal ceramic products having improved resistanceto failure by thermal shock andvery high strength at elevated temperatures.

In the search for materials capable of withstanding very high temperatures the possibility of combining the properties of metals and refractory oxides to advantage has not been overlooked. Materials composed in :part of metal and in part of refractory oxides have becomeavaib able and are known as metal ceramics. Among the more successful of these arecombinations of chromium and nited States Patent I chromium-alumina metal ceramics have found wide thermal shock.

The invention by means of which this object is attained is based on the discovery, that-the;-presence of a relatively'small quantityuof apartially reducible oxide selected from the group :consistingof titanium oxide, tantalum oxide and columbium oxide in the ceramic.- phase of a metal ceramic greatly enhances thestrength-of the material at high temperatures and imparts substantial improvement in resistance to thermal shock failure. The invention accordingly comprises a metalceramic containing oxide of titanium or tantalum or columbium or mixtures thereof in the ceramic constituent and having chromium in the metal constituent.

More specifically, the invention is a metal ceramic composed of 60% to 95% by volume of metal, the remainder ceramic. The metal constituent of the metal ceramic is chromium with which may be alloyed molybdenurn or tungsten or both. Because the atomicweight of tungsten is greater than that of molybdenum-expressed on a weight basis molybdenum is more effective than tungsten, but on an atomic basis, molybdenum and tungsten are substantially equivalent in the metal constituent. To point up this equivalency better, the proportions of the elements inthe metal constituentare expressed herein in terms of atomic percent. On this basis, molybdenumor tungsten, or both, may be present in the metal constituent up to 50 atom percent of the resulting alloy. The-ceramic constituent is composed of at least one oxide of ametal zrsasss selected from the group consisting of titanium, tantalum and columbium (referred to hereinafter as titanium group metal oxide) and may contain up to by weight of alumina. As will be explained with reference to Table Ibelow, oxide of titanium group metal constitutes at least ='0. 7 %by-.volume. of the metal ceramic.

Chromium in the metal constituent of the metal ceramic of the invention imparts oxidation resistance. By alloying with chromium suitable quantities of molybdenum or .tungsten or both, improved strength at high temperatures alloy of chromium and molybdenum or tungsten or both, 15.

it shouldcontain at least about 5 atom percent of tungsten or molybdenum or both.

As indicated, the ceramic constituent of the metal by volume. In such case the ceramic constituent is composed entirely of oxide of titanium,.tantalum', or columbium or mixtures thereof. Metal ceramics so constituted have the greatest strength at high temperatures yet achieved. However, such great strength is not required for all purposes, and it may be desirable to include in the ceramic constituent additional oxide so that in the final metal ceramic, oxide will constitute as much as 40% by volume. The additional oxide may'be alumina. The metal ceramics containing additional oxide are somewhat easier'to form than are those Withas little as 5% by volume of oxide.

In the manufacture of metal ceramics of the invention high purity powders of small particle size are desirable. Powders having a particle size of 10 microns and less are preferred but powders which pass through a 300 mesh screen (0.0018 inch openings) maybe used. Impurities known to cause embrittlement of the. metals should be avoided. 'Thus, carbon is detrimental, and should be kept to a minimum, preferably below 0.03%.

The constituent powders making up a particular composition may be mixed, formed and sintered or the metals may be pre-alloyedbefore mixing with the oxide. A

firing temperature between 1700 C. and 1900 C. in a dry hydrogen atmosphere has been found to produce excellent results in the sintering operation. Other protective atmospheres, such as argon, may be used.

The preparation of a typical material comprises, for example, preparing a charge of powder containing 50% tungsten, 40% chromium and 10% tantalum pentoxide by weight. On an atom percent basis, the metal constituent contains 26.5 atom percent of tungsten and 73.5 atom percent of chromium. The charge is wetball milled in benzene or toluene for from 24 to l00 hours and dried. A binder such as paraflin or gum arabic is incorporated,

"by slip-casting if desired, the materials having higher proportionsof oxide are more suited to forming by this method. The powdered constituents are mixed and added to a dilute hydrochloric acid solution to form a suitable slip. If relatively large quantities of molybdenum are used, hydrochloric acid alone is not a satisfactory peptizing agent because of its tendency to attack the molybdenum. For slip-casting metal ceramics containing molybdenum, it is therefore desirable to utilize an organic surface active agent as peptizer as disclosed in the co-pending application of L. A. Conant and D. M. Gillies, Serial No. 140,442, filedl'anuary 25, 1950. A preferred peptizing agent of this class is a solution of gum arabic.

Many formulations embodying the invention have been prepared and tested. Table I below sets forth a number of such formulations as specific examples. Of the compositions listed in Table I those containing no alumina were prepared by cold pressing, that is, the first of the 15 three methods explained above, and those containing alumina were slip-cast. All specimens were sintered in accordance with the procedure above described. In the table the compositions of the metal ceramics are given Constituent Weight, g. Density,

Volume, cc.

0.11 Volume percent Ta=O X100-0.7

Similar calculations using densities of 19.3 g./ cc. for tungsten; 4.26 g./cc. for TiOz and 4.60 for CbzOs show the volume percentage of titanium group oxide in compositions 19 to 29 inclusive to be, respectively: 1.4;, 1.4; 1.5; 3.0; 3.2; 0.7; 1.5; 3.8; 2.3; 7.6; and 3.8.

Table l Percent composition by weight Atom percent No. Pevrccnt Cl M W T103 T8105 011,0 A1303 CI M0 W 76 Nil Nil 24 N11 N11 N11 65 100 60 Nil Nil N11 40 N11 N ll 65 100 42 N11 52 N11 6 Nil Nil 92. 74 41 Nil 41 18 6 N11 N11 65 78 50 N ll 31 19 6 Nil Nil 65 85 30 N11 65 N11 5 N I1 Nil 93 62 30 N11 60 N11 N11 N11 87 64 40 N11 60 N11 10 N11 Nil 88 74 49 N 11 31 N11 N11 N11 65 85 53 42 N11 5 N11 N11 N11 90 71 49 39 N11 11 Nil Nil Nil 80 67 46 36 N11 18 Nil Nil Nil 70 70 73 24 N11 3 Nil Nil Nil 95 85 68 23 Nil 9 N11 N11 N11 85 85 66 22 N11 12 Nil Nil Nil 80 85 58 19 N11 23 N11 Nil Nil 65 85 57 19 Nil N11 N11 24 N11 65 85 53 9 17 21 N11 N11 N11 65 78 77 Nil Nil 1 N11 N11 22 65 100 73 Nil Ni 1 Ni N1 26 60 100 59 20 N i 1 N1 N1 21 65 84 59 20 N1 2 Ni Ni 20 65 84 44 N1 2 7 N1 N1 19 65 70 58 19 Ni Ni 1 Ni 21 65 85 58 19 Ni Ni 2 Ni 20 65 85 57 19 N1 N 1 N11 65 85 26 N l 60 1 Nil Ni 13 65 61 33 N1 42 N1 8 Ni 17 65 74 16 30 2 N1 N1 13 70 70 by .weight, and the volume percentage of the metal constituent (percent VM) in the metal ceramics is given. Also reported in the table is the composition of the metal constituent in atom percent.

It will be observed that in Table I compositions numbered 1 through 18 contain in the ceramic phase only oxide metal oxide in volume percentage is readily obtained by substraction from 100%. Thus in composition 13 with 95% by volume of metal, the proportion of titanium oxide in the metal ceramic is 5% by volume, Whereas in compositions 1, 2, 4, 5, 9 and 16 to 18 inclusive titanium group metal oxide constitutes 35% by volume of the metal ceramic. The other compositions of this group are intermediate of these extremes.

In compositions numbered 19 to 29 inclusive in Table I, the ceramic phase contains alumina in addition to titanium group metal oxide, and to determine the proportion of the latter requires different calculation. For example, composition No. 24 contains by weight, 58% chromium; 19% molybdenum; 1% tantalum pentoxide and 21% alumina. The volume of each constituent is determined by dividing the weight of each in grams by the density of the constituent. (In the following calculation the densities were Metal ceramics embodying the invention have been thoroughly tested to determine their capabilities. Typical results of some of the tests conducted on the specific compositions listed in Table I are tabulated below in Table II. These include hardness as measured on the .Rockwell A scale (RA), bend strength at 1000" C. and creep test results. In the last mentioned test, a specimen is subjected to a predetermined stress in bending at 1000 Y C., the stress is applied for the number of hours indicated,

and the deflection of the specimen is measured in inches. In the tests reported in Table II, the specimens used in No. 1 through 18 were /8 .inch by A inch by 1 inch in span. In the tests of specimens No. 19 through 29,

specimens were /3 inch by inch by 3 inches in span.

- In all cases the load was applied at the center of the span. Deflection is expressed in inch per inch (In./in.) span. As a measure of oxidation resistance, specimens are exposed for 200 hours at temperatures of 1000 C. or 1200" C. in air, cooled and then subjected to a bend test at 1000 C. The strength of the specimen after this treatment compared to its original strength at 1000 C. gives some indication of the extent of oxidation suffered by the specimen. Results of such tests are included in Table II. Also included in Table II are the is heate to 1000" C. and quenched in oil or water as times.

indicated, the heating and quenching cycle being repeated a number of times (indicated by Cyfin the table), and the strength of the specimen is then determined at 1000 C. Comparison with the original strength of a similar specimen indicates resistance to damage by thermal tain alumina in the ceramic phase are not so strong as those materials containing about 90% by volume of metal and having only titanium, tantalum, or columbium oxide in the ceramic phase, their creep resistance is better and their strength is superior to the conventional straight shock. chrormum-alumma materials.

Table II Strength at 1,000 0. Strength at l,000 0. Bending Creep in bending at 1,000 C. after 200 hrs. at after quench Hardness, strength temperature- No. Rx at 1,00010.

Stress Time hrs. Defl., p. s. 1. Temp. p. s. 1. 0y. p. s. i. In./1n.

as 40 1,000 $93 12% i 883 180 "5B "i "0: 143 1: 200 186 1 '10 as 240 0. 14a 1, 200 43 I 10 209 1,200 211 so 1,000 353 200 1,000 32 as 125 0.1 200 1,000 155 as 110 0.09 50 1,200 206 35 291 0.12 130 1,200 47 I 10 95 532 0.09 120 1,200 as I 10 g: 92 1,200 119 1,200 120 1,200 41 I 10 as 140 0.10 100 1,200 as 10 10a 10a 1, 200 100 117 1,200 73 10 $3 a .5 122 are 43 a :2 7s 75 30 108 01112 "BB "i300 a9 1 10 79 80 30 10s 0 200 00 1,200 49 I 10 2s 79 105 81 1,200 105 9 10 24..-.-- 79 02 10s 0. 005 52 1,200 49 7 s 25".-- 79 05 90 10s 0. 02a 01 1, 200 49 7 7 2a.... s0 a4 30 10s 0. 145 51 2 s 80 12s 98 r 10 2s 83 122 92 1, 000 100 98 1,200

In thousands.

1 Quenched in oil. 2 Quenched in water.

The average bend strength of commercially available chromium-alumina metal ceramics is of the order of 50,000 pounds per square inch. These materials have excellent oxidation resistance and exhibit substantially the same strength after exposure to temperatures of 1200 C. in air. However, the chromium-alumina materials are susceptible to thermal shock to the extent that they exhibit only about half their original strength after two or three cycles of heating and quenching. Also, they tend to exhibit considerable deflection under creep test conditions, for instance having a deflection of greater than 0.033 inch per inch under stress of 15,000 pounds per square inch at 1000 C. in 168 hours.

With the properties of the chromium-alumina materials in mind, it will be seen from the data in Table II that the metal ceramics of this invention are far stronger and generally much less subject to failure by thermal shock. Their creep properties are also much better in that they show less deflection under heavier loads applied for longer The oxidation resistance of the metal ceramics 0f the invention is generally very good, but, not unexpectedly, varies with the chromium content of the metal constituent, the higher the chromium content, the better the oxidation resistance. The data also show that the greater strength and greatest resistance to thermal shock .are generally attained with the higher proportions of metal and that of the materials listed in the table those containing tungsten or molybdenum alloyed with chromium generally have the greatest strength. While those :materials of about 65% by volume of metal which con- For greatest strength, therefore, a preferred range of composition for metal ceramics embodying the invention is about 85% to by volume of metal, the remainder ceramic, the metal being composed of chromium with which may be alloyed up to 50 atom percent of molybdenum or tungsten or both, the ceramic being oxide of titanium, tantalum or columbium or mixtures thereof. For easier fabrication, a preferred range of composition of metal ceramics embodying the invention is about 60% to 85% by volume of metal, the remainder ceramic, the metal being composed of chromium with which may be alloyed up to 50 atom percent of molybdenum or tungsten or both, the ceramic being oxide of titanium, tantalum or columbium or mixtures thereof and having associated therewith up to 95% by Weight of alumina in the ceramic phase, the oxide of titanium group metal constituting at least 0.7% by volume of the metal ceramic.

The reasons for the greatly improved physical properties ofthe metal ceramics of the invention as compared with the conventional chromium-alumina products are not entirely understood. However, it is believed that the improvement may be due to the partial reduction of titanium, tantalum, or columbium oxides during sintering. In chromium-alumina metal ceramics one has essentially a physical mixture of an oxide phase and a metal phase. It has been postulated that the A1203 reacts by solid solution formation with a thin layer of CI'aOa on the surface of the chromium particles to form a bond between metal and oxide. This postulate is reasonable isostructural, but the imporamount of such, chemical interaction must be small. Also, under the sintering conditions used the aluminum oxide is irreducible. In the materials of this invention, on the other hand, one purposely uses an oxide which is fairly easily reduced to a lower oxide (or oxides) but not easily reduced to the metal. During sintering, lower oxides may be formed in one or more of the following ways: (1) by thermal decomposition of the oxide, (2) by reaction of the oxide with metallic chromium to form chromium oxide and the lower oxide, (3) by reduction of the oxide by hydrogen in the furnace atmosphere. It is apparent that the final composition of the oxide phase may be complex, comprising the original oxide plus its reduction products plus chromium oxide and possibly the oxides of tungsten and/or molybdenum which may have been present on the original tungsten and molybdenum powders. Furthermore, theseoxides may combine to form solid solutions, euctectic structures or simple mixtures in the final oxide phase.

By studying sintering behavior and by examining microstructures and physical properties the following con'-' clusions have been drawn as to the functions of these partially reducible oxides in the formation of these materials:

(1) A liquid phase is formed during sintering even though the sintering temperature may be well below the melting points of any of the original constituents of their mixtures. This is presumably due to formation of lower melting oxide mixtures.

(2) This liquid phase promotes sintering and densification of the metal phase. Lower oxide melts are known to wet and dissolve metals more eflectively than normal oxide melts and hence might be expected toprovide a recrystallization medium for metal as well as for oxide.

(3) Chromium oxide, which normally occurs as an intergranular impurity in sintered chromium and sintered chromium alloys, is dissolved in the liquid phase and becomes part of the mixed oxide phase. This mixed oxide phase occurs in the final structure as more or less discrete grains so located as to be effective in stiffening the structure and imparting creep resistance to it.

(4) The final structure contains a somewhat larger proportion of oxide than would be expected on the basis of the original composition, due, presumably, to reaction between the added oxide and metallic chromium to form chromium oxide and the lower oxide.

Whether or not the foregoing theoretical explanation is correct, the fact remains that metal ceramics embodying the invention have strength at high temperature approaching the highest attained at room temperature by other materials. These properties endow these materials with great potential value for use in applications involving high stress at high temperature, for example, for turbine blades, rocket engine parts, extrusion dies and the like.

While a number of specific compositions embodying the invention have been given herein by way of example, the invention is not limited to those examples. Other metals which may be present in the metal constituent of metal ceramics according to the invention include columbium and tantalum which tend to improve toughness of the product.

Certain compositions embodying this invention are disclosed in my copending application Serial No. 360,453, filed June 9, 1953.

I claim:

1. A metal ceramic composed of 60% to 95% by volume of metal, the remainder ceramic, the metal constitutent of said metal ceramic being composed of chromium having alloyed therewith to 50 atom percent of at least one metal selected from the group consisting of molybdenum and tungsten; the ceramic constituent of said 'metal ceramic being composed of oxide of at least one .metal selected from the group consisting of titanium,

columbium, and tantalum and having associated there! with 0% to 95% by weight of alumina, said oxide of said titanium group metal constituting at least 0.7% by volume of said ,metalceramic. a

2. A metal ceramic composed of 60% to 95% by volume of metal, the remainder ceramic, the metal constituent of said .metal ceramic being composedof chromium having alloyed therewith 0 to atom percent of at least one metal selected from the group consisting of molybdenum and tungsten; said ceramic being oxide of at least one metal selected from thegijoup consisting of titanium, columbium, and tantalum.

3. .A metal ceramic composed of to 95% by volume of metal, the remainder ceramic, said metal being chromium; the ceramic constituent of said metal ceramic being composed of oxideof at' least one'metal selected from the group consisting of titanium, columbium,-and tantalum and having associated therewith 0% to.95%' by weight of alumina, said oxidev of said titanium group metal constituting at least 0.7% by volume ofsaid metal ceramic.

4. A'metal'cera'mic composed of 60% to 95%by volume of metal, the remainder ceramic, said metal being chromium; said ceramic being oxide of at least one metal selected from the group consisting of titanium, columbiurn and tantalum. h

5. A metal ceramic composed of to by volume ofmetaLthe .remainderceramic, the metal constituent of .saidmetal. ceramic being composed of chromium having alloyed therewith 0 to 50 atompercent of at leastone metal selected from the group consisting of molybdenum and tungsten; said ceramic being oxide of at least one metal selected from the group consisting of titaniumfiolumbium, and tantalum.

6. A metal ceramic composed of 85% to 95 by volume of metal, the remainder ceramic, said metal being chromium; said ceramic being oxide of at least one metal selected from the group consisting of titanium, columbium and tantalum V j V a :1

7. A metal ceramic composedof 85 to 95% byvolume of metal; the remainder ceramic, said metal'being chromium having alloyed therewith 5 to 50 atom percent of molybdenum; said ceramic being oxide of at least one metal selected from the group consisting of titanium, columbium, and tantalum.

8. A metal ceramic composed of 85 to 95% by volume of metal, the remainder ceramic, said metal being chromiumhaving alloyed therewith 5 to 50 atom percent of tungsten; said ceramic being oxide of at least one metal selected from the group consisting of titanium, columbium and tantalum.

9. A metal ceramic composed of 60% to 85 by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith 0 to 50 atom percent of at least one metal selected from the group consisting of molybdenum and tungsten; the ceramic constituent of said metal ceramic being composed of alumina and oxide of at least one 'metal selected from the group consisting of titanium, columbium, and tantalum, said oxide of said titanium group metal constituting at least 0.7% by volume of said metal ceramic,

10. A metal ceramic composed of 60% to 85% by volume of metal, the remainder ceramic, said metal being chromium; the ceramic constituent of said metal ceramic being composed of alumina and oxide of at least one metal selected from the group consisting of titanium, columbium, and tantalum, said oxide of said titanium group metal constituting at least 0.7% by volume of said metal ceramic.

11. A metal ceramic composed of 60% to 85% by volume or" metal, the remainder ceramic, said metal being chromium having alloyed therewith 5 to 50 atom percent of tungsten; the ceramic constituent of said metal ceramic being composed of alumina and oxide of at least one metal selected from the group consisting of titanium,

columbium, and tantalum, said oxide of said titanium group metal constituting at least 0.7% by volume of said metal ceramic.

12. A metal ceramic composed of 60% to 85% by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith 5 to 50 atom percent of molybdenum; the ceramic constituent of said metal ceramic being composed of alumina and oxide of at least one metal selected from the group consisting of titanium, columbium, and tantalum, said oxide of said titanium group metal constituting at least 0.7% by volume of said metal ceramic.

13. A metal ceramic composed of 60% to 95% by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith to 50 atom percent of at least one metal selected from the group consisting of molybdenum and tungsten; the ceramic constituent of said metal ceramic being composed of oxide of titanium having associated therewith up to 95% by weight of alumina, said oxide of titanium constituting at least 0.7% by volume of said metal ceramic.

14. A metal ceramic composed of 60% to 95 by volume of metal,the remainder ceramic, said metal being chromium; the ceramic constituent of said metal ceramic being composed of oxide of titanium having associated therewith up to 95% by weight of alumina, said oxide of titanium constituting at least 0.7% by volume of said metal ceramic.

15. A metal ceramic composed of 60% to 95% by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith to 50 atom percent of tungsten; the ceramic constituent of said metal ceramic being composed of oxide of titanium having associated therewith up to 95% by weight of alumina, said oxide of titanium constituting at least 0.7% by volume of said metal ceramic.

16. A metal ceramic composed of 60% to 95 by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith 5 to 50 atom percent of molybdenum; the ceramic constituent of said metal ceramic being composed of oxide of titanium having asso ciated therewith up to 95 by weight of alumina, said oxide of titanium constituing at least 0.7% by volume of said metal ceramic.

17. A metal ceramic composed of 60% to 85% by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith 0 to atom percent of at least one metal selected from the group consisting of molybdenum and tungsten; the ceramic constituent of said metal ceramic being composed of alumina and oxide of titanium, said oxide of titanium constituting at least about 0.7 by volume of said metal ceramic.

18. A metal ceramic composed of to by volume of metal, the remainder ceramic, said metal being chromium; the ceramic constituent of said metal ceramic being composed of alumina and oxide of titanium, said oxide of titanium constituting at least about 0.7% by volume of said metal ceramic.

19. A metal ceramic composed of 60% to'85% by volume of metal, the remainder ceramic, said metal beingchromium having alloyed therewith 5 to 50 atom percent tungsten; the ceramic constituent of said metal ceramic being composed of alumina and oxide of titanium, said oxide of titanium constituting at least about 0.7% by volume of said metal ceramic.

20. A metal ceramic composed of 60% to 85% by volume of metal, the remainder ceramic, said metal being chromium having alloyed therewith 5 to 50 atom percent of molybdenum; the ceramic constituent of said metal ceramic being composed of alumina and oxide of titanium, said oxide of titanium constituting at least about 0.7% by volume of said metal ceramic.

References Cited in the file of this patent UNITED STATES PATENTS 2,656,596 Conant et al. Oct. 27, 1953 FOREIGN PATENTS 645,681 Great Britain Nov. 8, 1950 676,441 Great Britain July 30, 1952 

1. A METAL CERAMIC COMPOSED OF 60% TO 95% BY VOLUME OF METAL, THE REMAINDER CERAMIC, THE METAL CONSTITUENT OF SAID METAL CERAMIC BEING COMPOSED OF CHROMIUM HAVING ALLOYED THEREWITH 0 TO 50 ATOM PERCENT OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN; THE CERAMIC CONSTITUENT OF SAID METAL CERAMIC BEING COMPOSED OF OXIDE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, COLUMBIUM, AND TANTALUM AND HAVING ASSOCIATED THEREWITH 0% TO 95% BY WEIGHT OF ALUMINA, SAID OXIDE OF SAID TATANIUM GROUP METAL CONSTITUTING AT LEAST 0.7% BY VOLUME OF SAID METAL CERAMIC. 